1. Field of the Invention
The present invention relates generally to an automated vehicular transmission system that includes an engine, a multiple ratio transmission, a centrifugally operated master friction clutch for drivingly coupling the engine to the transmission and a control system for controlling engine output torque.
2. Description of the Related Art
Automated mechanical transmission systems not requiring the vehicle driver to operate the vehicle master clutch (so called “two-pedal systems”) are known in the art. To reduce the complexity of these systems, it has been known to provide a centrifugally operated friction clutch for drivingly coupling a vehicle engine to the transmission. Centrifugally operated friction clutches typically include weights pivotable or rotatable with respect to an engine driven input member that, upon rotation of an input member, will move radially outwardly under the effect of centrifugal force to cause the input member to frictionally engage an output member.
When the centrifugal master friction clutch is engaged and rotational torque is being transmitted from the vehicle engine to the transmission, there generally is a large torque load or “torque lock” holding the transmission gears in a particular position. This torque load makes it quite difficult, if not impossible, to shift the transmission to neutral or change gears without somehow significantly reducing the torque load.
One way to relieve torque load is to disengage the master clutch, which breaks the coupling between the input member and the output member. Disengaging the master friction clutch permits the torque load to go to zero and allows the operator or transmission system to shift into neutral or change gears. However, disengaging a centrifugally operated clutch requires a substantial reduction in the engine speed. If the engine is generating substantial, uninterrupted power at an engine speed above the engagement speed of the centrifugally operated clutch, it may be difficult or impossible to achieve neutral or shift gears in the transmission. Also, shifting the transmission with the master friction clutch remaining engaged is preferred in many situations, as such shifts tend to be of a higher shift quality and/or cause less wear on the drive-line.
Accordingly, a control system and method of operating a vehicular transmission system is required that breaks torque load between the engine and the transmission when the engine is generating substantial, uninterrupted power.